The invention relates to the field of optical waveguiding, and in particular to an omnidirectional multilayered device for enhanced waveguiding of electromagnetic radiation.
Mirrors are probably the most prevalent of optical devices. Known to the ancients and used by them as objects of worship and beauty, mirrors are currently employed for imaging, solar energy collection and in laser cavities. Their intriguing optical properties have captured the imagination of scientists as well as artists and writers.
One can distinguish between two types of mirrors, the age-old metallic, and more recent dielectric. Metallic mirrors reflect light over a broad range of frequencies incident from arbitrary angles, i.e., omnidirectional reflectance. However, at infrared and optical frequencies, a few percent of the incident power is typically lost due to absorption. Multilayer dielectric mirrors are used primarily to reflect a narrow range of frequencies incident from a particular angle or particular angular range. Unlike their metallic counterparts, dielectric reflectors can be extremely low loss.
The ability to reflect light of arbitrary angle of incidence for all-dielectric structures has been associated with the existence of a complete photonic bandgap, which can exist only in a system with a dielectric function that is periodic along three orthogonal directions. In fact, a recent theoretical analysis predicted that a sufficient condition for the achievement of omnidirectional reflection in a periodic system with an interface is the existence of an overlapping bandgap regime in phase space above the light cone of the ambient media.
The theoretical analysis is now extended to provide experimental realization of a multilayer omnidirectional reflector operable in infrared frequencies. The structure is made of thin layers of materials with different dielectric constants (polystyrene and tellurium) and combines characteristic features of both the metallic and dielectric mirrors. It offers metallic-like omnidirectional reflectivity together with frequency selectivity and low-loss behavior typical of multilayer dielectrics.
Accordingly, in accordance with the invention there is provided a device having at least one inner core region in which electromagnetic radiation is confined, and at least two outer regions surrounding the inner core region, each with a distinct refractive index. The outer regions confine electromagnetic radiation within the inner core region. The refractive indices, the number of outer regions, and thickness of the outer regions result in a reflectivity for a planar geometry that is greater than 95% for angles of incidence ranging from 0xc2x0 to at least 80xc2x0 for all polarizations for a range of wavelengths of the electromagnetic radiation. In exemplary embodiments, the inner core region is made of a low dielectric material, and the outer regions include alternating layers of low and high dielectric materials. In one aspect of the invention, the device is a waveguide, and in another aspect the device is a microcavity.